1. Field of the Invention
Exemplary embodiments of the present invention relate to a light-emitting diode (LED) driver and, more particularly, to an LED driver to power LEDs with an alternating current (AC) voltage source without an AC/DC converter.
2. Discussion of the Background
A light-emitting diode (LED) is a semiconductor light source, which is turned on is at a forward-bias threshold voltage or higher when the LED is forward-biased. Further, an anti-parallel LED pair may be used to extend an operating region when an AC voltage source is applied. The anti-parallel LED pair may operate during the positive half-cycle and the negative half-cycle of the AC voltage source. In this case, one of the anti-parallel LED pair is forward-biased at a forward-bias threshold voltage or higher during the positive half-cycle of the AC voltage source, and the other of the anti-parallel LED pair is forward-biased at a forward-bias threshold voltage or higher during the negative half-cycle of the AC voltage source. This mode of operating the anti-parallel LED pair may cause the LEDs to have a low light-emitting efficiency of 50% or less or to suffer severe flicker.
In addition, since LEDs are turned on at a forward-bias threshold voltage or higher, LEDs other than the anti-parallel LED pair may require an additional AC/DC converter. Thus, designing an LED driver with the additional AC/DC converter may lead to increased costs and a more complex circuit configuration. Further, a conventional solution using only a rectifier circuit or smoothing circuit may limit the number of LEDs connected in series. Accordingly, an LED driver that solves these problems is needed.